1. Field of the Invention
The present invention relates to an organic light emitting display and a driving method thereof and, more particularly, to an organic light emitting display and a driving method thereof that ensure an operation margin of a driving circuit when driving a large-size panel by applying an interlaced scanning method, prevent a voltage drop (IR-drop) of a first power source line VDD and, simultaneously, minimize degradation of the organic light emitting diode OLED in a pixel circuit of the organic light emitting display by dividing a data write period from a light emission period in driving the panel.
2. Discussion of Related Art
Recently, the organic light emitting display has attracted attention as the next generation flat panel display due to its advantages such as a thin thickness, a wide viewing angle, a high response rate, etc. Such an organic light emitting display controls the amount of current flowing in the organic light emitting diodes of the respective pixels to control the brightness of the respective pixels, thus displaying an image. That is, a current corresponding to a data voltage is supplied to the organic light emitting diode and thereby the organic light emitting diode emits light correspondingly to the supplied current. Here, the data voltage applied has multilevel values in a predetermined range so as to express gradation.
If a thin film transistor TFT using amorphous silicon (a-si) is used as a driving transistor, the current driving capability is relatively low; however, it has advantages in that the uniformity of the display device is excellent and it is more favorable to a large-size process.
As driving methods for driving such an organic light emitting diode display, there are a progressive scanning method and an interlaced scanning method. The progressive scanning method drives scan lines in sequence from top left to bottom right of a screen, in which an image is displayed on all horizontal lines in one frame at one time.
The interlaced scanning method displays only the half of the horizontal lines in one image frame and this method may scan an image by dividing one image frame into two fields (odd and even) or may scan an image by dividing two frames into a first frame (odd) and a second frame (even).
If using the progressive scanning method, it has an advantage in that it provides an excellent image quality in a static screen; however, it also has drawbacks in that it is difficult to ensure an operation margin of a driving circuit when driving a large-size panel, since its scanning rate is no more than half that of the interlaced scanning method. Moreover, the progressive scanning method has drawbacks in that it may cause a voltage drop (IR-drop) as a first power source line VDD passes through the respective pixel circuits, thus decreasing the brightness of the pixels gradually. Furthermore, in the general organic light emitting diode display, as current flows in one direction from an anode to a cathode of the organic light emitting diode OLED, space charges are stored between a hole transport layer HTL and an emitting layer EML or between an electron transport layer ETL and an emitting layer EML. Due to the accumulation of the space charges, the current IOLED flowing in the organic light emitting diode OLED may be dropped. Accordingly, as the brightness of the respective pixels may be decreased, the brightness of the organic light emitting display applying the pixel circuits is lowered gradually with time. Furthermore, the lifespan of the organic light emitting display may be shortened. In addition, due to the difference of the degradation degrees of the organic light emitting diodes in the respective pixel circuits, the brightness of the whole organic light emitting display becomes non-uniform as a result.